Heretofore, various proposals have been made with respect to catalysts for gas phase catalytic oxidation of propylene with molecular oxygen to produce acrolein and acrylic acid, and catalysts for gas phase catalytic oxidation of isobutylene with a molecular oxygen-containing gas to produce methacrolein and methacrylic acid.
These catalysts are, of course, required to be able to produce the corresponding unsaturated aldehyde and unsaturated carboxylic acid in good yield, but also required to have sufficiently high mechanical strength and durability durable for industrial use for a long period of time.
Heretofore, in order to improve the performance of the catalyst to be used for such a reaction, it has been proposed to control the specific surface area, average pore radius, or pore volume, etc. of the catalyst within specific ranges. For example, patent document 1 proposes to control the specific surface area of a catalyst to be from 100 to 250 m2/g; patent document 2 proposes to control the pore volume to be from 0.2 to 0.4 ml/g and the average pore radius to be 2000 Å; and patent document 3 proposes to control the specific surface area to be from 5 to 20 m2/g, the average pore diameter to be from 0.1 to 0.9 μm and the pore volume to be from 0.3 to 0.9 ml/g.
Further, it has been proposed to improve the performance or the mechanical strength of the catalyst by controlling the conditions for drying or calcination in the production of the catalyst. For example, patent document 4 or patent document 5 proposes to carry out calcination at a temperature of from 550 to 750° C. stepwisely, or to carry out multi-stage calcination by preliminarily carrying out preparatory calcination and further carrying out the main calcination.
By such prior art, certain effects can be obtained, but they are not necessarily satisfactory. Accordingly, a new catalyst which is capable of easily improving the performance of the catalyst and which is excellent in reproducibility, and a process for its production, are still desired.
Patent Document 1: JP-B-53-5632
Patent Document 2: JP-B-6-7924
Patent Document 3: JP-A-57-119837
Patent Document 4: JP-B-55-36384
Patent Document 5: JP-B-56-28180